The effect of moisture on nitrous oxide emissions from soil and the N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio under laboratory conditions

Nitrous oxide (N₂O) contributes to greenhouse effect; however, little information on the consequences of different moisture levels on N₂O/(N₂O+N₂) ratio is available. The aim of this work was to analyze the influence of different soil moisture values and thus of redox conditions on absolute and relative emissions of N₂O and N₂ at intact soil cores from a Vertic Argiudoll. For this reason, the effect of water-filled porosity space (WFPS) values of soil cores of 40, 80,100, and 120% (the last one with a 2-cm surface water layer) was investigated. The greatest N₂O emission occurred at 80% WFPS treatment where conditions were not reductive enough to allow the complete reduction to N₂. The N₂O/(N₂O+N₂) ratio was lowest (0–0.051) under 120% WFPS and increased with decreasing soil moisture content. N₂O/(N₂O+N₂) ratio values significantly correlated with soil Eh; redox conditions seemed to control the proportion of N gases emitted as N₂O. N₂O emissions did not correlate satisfactorily with N₂O/(N₂O+N₂) ratio values, whereas they were significantly explained by the amount of total N₂O+N₂ emissions.     

Soil N<Subscript>2</Subscript>O emissions and N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio as affected by different fertilization practices and soil moisture

The objective of this work was to evaluate the effect of the chemical nature and application frequency of N fertilizers at different moisture contents on soil N₂O emissions and N₂O/(N₂O+N₂) ratio. The research was based on five fertilization treatments: unfertilized control, a single application of 80 kg ha⁻¹ N-urea, five split applications of 16 kg ha⁻¹ N-urea, a single application of 80 kg ha⁻¹ N–KNO₃, five split applications of 16 kg ha⁻¹ N–KNO₃. Cumulative N₂O emissions for 22 days were unaffected by fertilization treatments at 32% water-filled pore space (WFPS). At 100% and 120% WFPS, cumulative N₂O emissions were highest from soil fertilized with KNO₃. The split application of N fertilizers decreased N₂O emissions compared to a single initial application only when KNO₃ was applied to a saturated soil, at 100% WFPS. Emissions of N₂O were very low after the application of urea, similar to those found at unfertilized soil. Average N₂O/(N₂O+N₂) ratio values were significantly affected by moisture levels (p = 0.015), being the lowest at 120% WFPS. The N₂O/(N₂O+N₂) ratio averaged 0.2 in unfertilized soil and 0.5 in fertilized soil, although these differences were not statistically significant.     

Cultivable heterotrophic N<Subscript>2</Subscript>-fixing bacterial diversity in rice fields in the Yangtze River Plain

Heterotrophic N₂-fixing bacteria are a potentially important source of N₂ fixation in rice fields due to the moist soil conditions. This study was conducted at eight sites along a geographic gradient of the Yangtze River Plain in central China. A nitrogen-free solid malate-sucrose medium was used to isolate heterotrophic N₂-fixing bacteria. Numbers of the culturable N₂-fixing bacteria expressed as CFU (colony forming units) ranged between 1.41ǂ.42᎒⁶ and 1.24ǂ.23᎒⁸ in the sampled paddy field sites along the plain. Thirty strains with high ARA (acetylene reduction activity) were isolated and purified; ARA of the strains varied from 0.9 to 537.8 nmol C₂H₄ culture^-1 h^-1, and amounts of ¹⁵N fixed ranged between 0.008 and 0.4866 mg·culture^-1·day^-1. According to morphological and biochemical characteristics, 14 strains were identified as the genus Bacillus, 2 as Burkholderia, 1 as Agrobacterium, 4 as Pseudomonas, 2 as Derxia, 1 as Alcaligenes, 1 as Aeromonas, 2 as Citrobacter, and 3 strains belonged to the corynebacter-form group.     

A bradyrhizobial-<Emphasis Type="Italic">Penicillium</Emphasis> spp. biofilm with nitrogenase activity improves N<Subscript>2</Subscript> fixing symbiosis of soybean

A bradyrhizobial-fungal biofilm (i.e. Bradyrhizobium elkanii SEMIA 5019-Penicillium spp.) developed in vitro was assayed for its nitrogenase activity and was evaluated for N₂-fixing symbiosis with soybean under greenhouse conditions. The biofilm showed nitrogenase activity, but the bradyrhizobial strain alone did not. Shoot and root growth, nodulation and N accumulation of soybean increased significantly with an inoculum developed from the biofilm. This study concludes that such biofilmed inoculants can improve N₂-fixing symbiosis in legumes, and can also directly contribute to soil N fertility in the long term. Further studies should be conducted to investigate the performance of these inoculants under field conditions.     

Estimating N transfers between N<Subscript>2</Subscript>-fixing actinorhizal species and the non-N<Subscript>2</Subscript>-fixing<Emphasis Type="Italic"> Prunus avium</Emphasis> under partially controlled conditions

Two methods of N transfer between plants—by litter decomposition and root-to-root exchange—were examined in mixed plantations of N-fixing and non-fixing trees. Nitrogen transfers from decaying litters were measured by placing ¹⁵N-labelled litters from four actinorhizal tree species around shoots of containerized Prunus avium. Nitrogen transfers by root-to-root exchanges were measured after foliar NO₃-¹⁵N fertilization of Alnus subcordata and Elaeagnus angustifolia growing in containers in association with P. avium. During the first 2 years of litter decomposition, from 5–20% of the N, depending on the litter identity, was released and taken up by P. avium. N availability in the different litters was strongly correlated with the amount of water-soluble N, which was highest in leaves of E. angustifolia. In the association between fixing and non-fixing plants, 7.5% of the A. subcordata N and 25% of E. angustifolia N was transferred to P. avium by root exchange. These results showed that the magnitude of N transfers by root exchange depended on the associated N₂-fixing species. Among the species investigated, E. angustifolia displayed the highest capacity for exudating N from roots as well as for releasing N from litters. These qualities make this tree a promising species for enhancing wood yields in mixed stands.     

N<Subscript>2</Subscript>O emission from conventional and minimum-tilled soils

In this study, we investigated N₂O emissions from two fields under minimum tillage, cropped with maize (MT maize) and summer oats (MT oats), and a conventionally tilled field cropped with maize (CT maize). Nitrous oxide losses from the MT maize and MT oats fields (5.27 and 3.64 kg N₂O-N ha⁻¹, respectively) were significantly higher than those from the CT maize field (0.27 kg N₂O-N ha⁻¹) over a period of 1 year. The lower moisture content in CT maize (43% water-filled pore space [WFPS] compared to 60–65%) probably caused the difference in total N₂O emissions. Denitrification was found to be the major source of N₂O loss. Emission factors calculated from the MT field data were high (0.04) compared to the CT field (0.001). All data were simulated with the denitrification decomposition model (DNDC). For the CT field, N₂O and N₂O + N₂ emissions were largely overestimated. For the MT fields, there was a better agreement with the total N₂O and N₂O + N₂ emissions, although the N₂O emissions from the MT maize field were underestimated. The simulated N₂O emissions were particularly influenced by fertilization, but several other measured N₂O emission peaks associated with other management practices at higher WFPS were not captured by the model. Several mismatches between simulated and measured \textNH₄⁺ {\text{NH}}_4^ + , \textNO₃^- {\text{NO}}_3^ - and WFPS for all fields were observed. These mismatches together with the insensitivity of the DNDC model for increased N₂O emissions at the management practices different from fertilizer application explain the limited similarity between the simulated and measured N₂O emissions pattern from the MT fields.     

Effects of biochar addition on N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions from two paddy soils

Impacts of biochar addition on nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from paddy soils are not well documented. Here, we have hypothesized that N₂O emissions from paddy soils could be depressed by biochar incorporation during the upland crop season without any effect on CO₂ emissions. Therefore, we have carried out the 60-day aerobic incubation experiment to investigate the influences of rice husk biochar incorporation (50 t ha⁻¹) into two typical paddy soils with or without nitrogen (N) fertilizer on N₂O and CO₂ evolution from soil. Biochar addition significantly decreased N₂O emissions during the 60-day period by 73.1% as an average value while the inhibition ranged from 51.4% to 93.5% (P < 0.05–0.01) in terms of cumulative emissions. Significant interactions were observed between biochar, N fertilizer, and soil type indicating that the effect of biochar addition on N₂O emissions was influenced by soil type. Moreover, biochar addition did not increase CO₂ emissions from both paddy soils (P > 0.05) in terms of cumulative emissions. Therefore, biochar can be added to paddy fields during the upland crop growing season to mitigate N₂O evolution and thus global warming.     

Time course of N<Subscript>2</Subscript> fixation and growth of chickpea

The ¹⁵N isotopic dilution technique was used to assess N₂ fixation in desi chickpea (Cicer arientinum L.) cv. Myles at different growth stages as influenced by inoculation method. In this growth chamber study, no significant differences in nodule dry weight, amount of N₂ fixed and plant dry matter were observed between seed inoculation with seed-applied peat inoculant and soil-applied granular inoculant placed 2.5 cm below the seed. However, seed inoculation with liquid inoculant was inferior to the seed-applied peat or the granular inoculant for all parameters measured at all sampling dates. The seed-applied peat and granular inoculant treatments fixed 4.8 and 4.1 mg N plant^-1, respectively, by the late vegetative stage, and reached a maximum of 20.6 and 25.6 mg N plant^-1, respectively, by the late pod-filling stage. These values accounted for 30.5% and 34.9% of the total plant N for the peat and granular inoculant, respectively, by late pod-filling. For the liquid inoculant treatment, the amount of N₂ fixed increased from 2.3 mg N plant^-1 by the late vegetative stage to a maximum of 9.6 mg N plant^-1 which was 22.2% of total plant N by the mid pod-filling stage. The highest daily N₂ fixation rate for the peat and granular inoculant was 0.9 mg N plant^-1 and occurred between flowering and early pod-filling, whereas that for the liquid occurred between early and mid pod-filling stages (0.23 mg N plant^-1). After the mid pod-filling stage, little or no N₂ was fixed in all treatments. Plant dry matter increased from the late vegetative stage to physiological maturity but the greatest dry matter accumulation occurred between the late vegetative and early pod-filling stages in all treatments.     

Improved Photodegradation Efficiency of 2,4-DCP Through a Combined Q<Subscript>3</Subscript>Fe(III)-Decorated Porous g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>/H<Subscript>2</Subscript>O<Subscript>2</Subscript> System

Graphitic carbon nitride (g-C₃N₄) is a photocatalyst with wide application in removal of organic pollutants. In this study, we designed a porous g-C₃N₄ (p-g-C₃N₄)/8-quinolinolato iron(III) (Q₃Fe)/H₂O₂ system to enhance the organic pollutant removal efficiency by combining photocatalysis and Fenton interaction under neutral condition. The p-g-C₃N₄ was prepared through a two-step thermal oxidation reaction. Afterwards, Q₃Fe-coupled p-g-C₃N₄ was prepared by an impregnating method. The 2,4-dichlorophenol (2,4-DCP) photodegradation ratio and decomposition rate of the p-g-C₃N₄/Q₃Fe/H₂O₂ system are approximately 5 and 18 times as high as those of individual p-g-C₃N₄ system, respectively. Besides, its degradation rate is 4.3 times as high as that in the p-g-C₃N₄/H₂O₂ system. Meanwhile, Q₃Fe/g-C₃N₄ also exhibits higher activity than individual p-g-C₃N₄ in 2,4-DCP photo-decomposing. On the basis of the results of the radical trapping experiments and the Fe(II) concentration in different systems, the synergistic effect between photocatalysis and Fenton reaction is vital for the efficient pollutant degradation. The coupled system combining p-g-C₃N₄ with Q₃Fe and H₂O₂ shows potential for efficient treatment of recalcitrant organic pollutants. The combined system in this work indicated a new idea for the decomposition of organic pollutants.     

Suppression of NH<Subscript>3</Subscript> and N<Subscript>2</Subscript>O emissions by massive urea intercalation in montmorillonite

Purpose  

A large amount of nitrogen (N) fertilizers has been broadcasted over soil surface for reliable crop production. Unfortunately, the broadcasted N vulnerable to volatilization and leaching can lead to serious environmental problems. As a new approach to mitigate N loss of broadcasted fertilizers, massive intercalation of urea into montmorillonite (MMT) was recently proposed to innovatively enhance the urea use efficiency. This study focuses on demonstrating the behaviors of the urea intercalated into MMT in soils.     

N<Subscript>2</Subscript>O,CO<Subscript>2</Subscript>, Production,and C Sequestration in Vineyards: a Review

Even if it is less polluting than other farm sectors, grape growing management has to adopt measures to mitigate greenhouse gas (GHG) emissions and to preserve the quality of grapevine by-products. In viticulture, by land and crop management, GHG emissions can be reduced through adjusting methods of tillage, fertilizing, harvesting, irrigation, vineyard maintenance, electricity, natural gas, and transport until wine marketing, etc. Besides CO₂, nitrous oxide (N₂O) and methane (CH₄), released from fertilizers and waste/wastewater management are produced in vineyards. As the main GHG in vineyards, N₂O can have the same harmful action like large quantities of CO₂. Carbon can be found in grape leaves, shoots, and even in fruit pulp, roots, canes, trunk, or soil organic matter. C sequestration in soil by using less tillage and tractor passing is one of the efficient methods to reduce GHG in vineyards, with the inconvenience that many years are needed for detectable changes. In the last decades, among other methods, cover crops have been used as one of the most efficient way to reduce GHG emissions and increase fertility in vineyards. Even if we analyze many references, there are still limited information on practical methods in reducing emissions of greenhouse gases in viticulture. The aim of the paper is to review the main GHG emissions produced in vineyards and the approached methods for their reduction, in order to maintain the quality of grapes and other by-products.     

An assessment of factors controlling N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions from crop residues using different measurement approaches

Management of plant residues plays an important role in maintaining soil quality and nutrient availability for plants and microbes. However, there is considerable uncertainty regarding the factors controlling residue decomposition and their effects on greenhouse gas (GHG) emissions from the soil. This uncertainty is created both by the complexity of the processes involved and limitations in the methodologies commonly used to quantify GHG emissions. We therefore investigated the addition of two soil residues (durum wheat and faba bean) with similar C/N ratios but contrasting fibres, lignin and cellulose contents on nutrient dynamics and GHG emission from two contrasting soils: a low-soil organic carbon (SOC), high pH clay soil (Chromic Haploxerert) and a high-SOC, low pH sandy-loam soil (Eutric Cambisol). In addition, we compared the effectiveness of the use of an infrared gas analyser (IRGA) and a photoacoustic gas analyser (PGA) to measure GHG emissions with more conventional gas chromatography (GC). There was a strong correlation between the different measurement techniques which strengthens the case for the use of continuous measurement approaches involving IRGA and PGA analyses in studies of this type. The unamended Cambisol released 286% more CO₂ and 30% more N₂O than the Haploxerert. Addition of plant residues increased CO₂ emissions more in the Haploxerert than Cambisol and N₂O emission more in the Cambisol than in the Haploxerert. This may have been a consequence of the high N stabilization efficiency of the Haploxerert resulting from its high pH and the effect of the clay on mineralization of native organic matter. These results have implication management of plant residues in different soil types.     

Nitrogen transformation rates and N<Subscript>2</Subscript>O producing pathways in two pasture soils

Purpose

Better understanding of N transformations and the regulation of N₂O-related N transformation processes in pasture soil contributes significantly to N fertilizer management and development of targeted mitigation strategies.

Materials and methods

¹⁵N tracer technique combined with acetylene (C₂H₂) method was used to measure gross N transformation rates and to distinguish pathways of N₂O production in two Australian pasture soils. The soils were collected from Glenormiston (GN) and Terang (TR), Victoria, Australia, and incubated at a soil moisture content of 60% water-filled pore space (WFPS) and at temperature of 20 °C.

Results and discussion

Two tested pasture soils were characterized by high mineralization and immobilization turnover. The average gross N nitrification rate (n_tot) was 7.28 mg N kg^?1 day^?1 in TR soil () and 5.79 mg N kg^?1 day^?1 in GN soil. Heterotrophic nitrification rates (n_h), which accounting for 50.8 and 41.9% of n_tot, and 23.4 and 30.1% of N₂O emissions in GN and TR soils, respectively, played a role similar with autotrophic nitrification in total nitrification and N₂O emission. Denitrification rates in two pasture soils were as low as 0.003–0.004 mg N kg^?1 day^?1 under selected conditions but contributed more than 30% of N₂O emissions.

Conclusions

Results demonstrated that two tested pasture soils were characterized by fast N transformation rates of mineralization, immobilization, and nitrification. Heterotrophic nitrification could be an important NO₃^?–N production transformation process in studied pasture soils. Except for autotrophic nitrification, roles of heterotrophic nitrification and denitrification in N₂O emission in two pasture soils should be considered when developing mitigation strategies.

     

Effect of soil water status and mulching on N<Subscript>2</Subscript>O and CH<Subscript>4</Subscript> emission from lowland rice field in China

Cultivation of rice in unsaturated soils covered with mulch is receiving more attention in China because of increasingly serious water shortage; however, greenhouse gas emission from this cultivation system is still poorly understood. A field experiment was conducted in 2001 to compare nitrous oxide (N₂O) and methane (CH₄) emission from rice cultivated in unsaturated soil covered with plastic or straw mulch and the traditional waterlogged production system. Trace gas fluxes from the soil were measured weekly throughout the entire growth period using a closed chamber method. Nitrous oxide emissions from unsaturated rice fields were large and varied considerably during the rice season. They were significantly affected by N fertilizer application rate. In contrast, N₂O emission from the waterlogged system was very low with a maximum of 0.28 mg N₂O m^–2 h^–1. However, CH₄ emission from the waterlogged system was significantly higher than from the unsaturated system, with a maximum emission rate of 5.01 mg CH₄ m^–2 h^–1. Our results suggested that unsaturated rice cultivation with straw mulch reduce greenhouse gas emissions.     

Effect of Stover Management and Nitrogen Fertilization on N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> Emissions from Irrigated Maize in a High Nitrate Mediterranean Soil

A high soil nitrogen (N) content in irrigated areas quite often results in environmental problems. Improving the management practices of intensive agriculture can mitigate greenhouse gas (GHG) emissions. This study compared the effect of maize stover incorporation or removal together with different mineral N fertilizer rates (0, 200 and 300 kg N ha^?1) on the emission of nitrous oxide (N₂O) and carbon dioxide (CO₂) on a sprinkler-irrigated maize (Zea mays L.). The trail was conducted in the Ebro Valley (NE Spain) in a high nitrate-N soil (i.e. 200 g NO₃–N kg^?1). Nitrous oxide and CO₂ emissions were sampled weekly using a semi-static closed chamber and quantified using the photoacoustic technique in 2011 and 2012. Applying sidedress N fertilizer tended to increase N₂O emissions whereas stover incorporation did not have any clear effect. Nitrification was probably the main process leading to N₂O. Denitrification was limited by the low soil moisture content (WFPS <?54%), due to an adequate irrigation management. Emissions ranged from ??0.11 to 0.36% of the N applied, below the IPCC (2007) values. Nitrogen fertilization tended to reduce CO₂ emission, but only in 2011. Stover incorporation increased CO₂ emission. Nitrogen use efficiency decreased with increasing mineral fertilizer supply. The application of N in high N soils of the Ebro Valley is not necessary until the soil restores a normal mineral N content, regardless of stover management. This will combine productivity with keeping N₂O and CO₂ emissions under control provided irrigation is adequately managed. Testing soil NO₃ ^?–N contents before fertilizing would improve N fertilizer recommendations.     

The fungal and bacterial biomass (selective inhibition) and the production of CO<Subscript>2</Subscript> and N<Subscript>2</Subscript>O by soddy-podzolic soils of postagrogenic biogeocenoses

In the humus horizon of soddy-podzolic soils of postagrogenic cenoses and primary forests, the contributions of the fungi and bacteria were determined by the selective inhibition of the substrate-induced respiration (SIR) by antibiotics; the basal (microbial) respiration and the net-produced nitrous oxide (N₂O) were also determined. The procedure of the SIR separation using antibiotics (cycloheximide and streptomycin) into the fungal and bacterial components was optimized. It was shown that the fungi: bacteria ratio was 1.58, 2.04, 1.55, 1.39, 2.09, and 1.86 for the cropland, fallow, and different-aged forests (20, 45, 90, and 450 years), respectively. The fungal and bacterial production of CO₂ in the primary forest soil was higher than in the cropland by 6.3 and 11.4 times, respectively. The production of N₂O in the soils of the primary and secondary (90-year-old) forests (3 and 7 ng N-N₂O/g soil per hour, respectively) was 2–13 times lower than in the postagrogenic cenoses, where low values were also found for the microbial biomass carbon (C_mic), its components (the C_mic-bacteria and C_mic-fungi), and the portion of C_mic in the organic carbon of the soil. A conclusion was drawn about the misbalance of the microbial processes in the overgrown cropland accompanied by the increased production of N₂O by the soil during its enrichment with an organic substrate (glucose).     

Long-term animal impact modifies potential production of N<Subscript>2</Subscript>O from pasture soil

At cattle overwintering areas, inputs of nutrients in animal excrements create conditions favourable for intensive microbial activity in soil. During nitrogen transformations, significant amounts of N₂O are released, which makes overwintering areas important sources of N₂O emission. In previous studies, however, increasing intensity of long-term cattle impact did not always increase emissions of N₂O from the soil: in some cases, N₂O emissions from the soil were lower at the most impacted area than at the moderately impacted one. Thus, the relationships between the level of long-term animal impact and potential production of N₂O from soil by denitrification were investigated in field and laboratory experiments. Field measurements indicated that the production of N₂O after glucose and nitrate amendments was greater in severely and moderately impacted locations than in an unimpacted location, while differences between the severely and moderately impacted locations were not significant. In laboratory experiments, the potential production of N₂O (measured as anaerobic production of N₂O after addition of glucose and nitrate) was highest in the moderately impacted soil. Surprisingly, potential N₂O production was lower in the most impacted than in the moderately impacted soil, and the net N₂O production in the highly impacted soil was further decreased by a significant reduction of N₂O to N₂. The expected stimulating effect of an increasing ratio of glucose C to nitrate N on the reduction of N₂O to N₂ during denitrification was not confirmed. The results show that cattle increase the denitrification potential of the soil but suggest that the denitrification potential does not increase indefinitely with increasing cattle impact.     

Net and gross mineral N production rates at three levels of forest canopy retention: evidence that NH<Subscript>4</Subscript><Superscript>+</Superscript> and NO<Subscript>3</Subscript><Superscript>−</Superscript> dynamics are uncoupled

Alternative silvicultural systems were introduced in Coastal Western Hemlock forests of British Columbia, Canada, to reduce disturbance incurred by conventional clear-cutting and to maintain the forest influence on soil nutrient cycling. As we hypothesized, in situ pools and net mineralization of NH₄ ⁺ were lower under no and low disturbance (old-growth forest and shelterwood) compared to clear-cuts (high disturbance); in situ pools and net production of NO₃ ⁻ were very low across all treatments. Gross transformation rates of NH₄ ⁺ increased while those of NO₃ ⁻ decreased with increasing disturbance, suggesting that these processes were uncoupled. We conclude that shelterwood harvesting reduces the impact on forest floor NH₄ ⁺ cycling compared to clear-cutting, and that neither low nor high disturbance intensity results in substantial NO₃ ⁻ accumulation, as what occasionally occurs in other ecosystems. We hypothesize that the uncoupling of NH₄ ⁺ and NO₃ ⁻ dynamics may be due to the predominance of heterotrophic nitrification by lignin-degrading fungi that oxidize organic N rather than NH₄ ⁺–N, and whose activities are suppressed at high NH₄ ⁺ concentrations.     

Increases in soil CO<Subscript>2</Subscript> and N<Subscript>2</Subscript>O emissions with warming depend on plant species in restored alpine meadows of Wugong Mountain,China

Purpose

Ecosystem restorations can impact carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions which are important greenhouse gasses. Alpine meadows are degraded worldwide, but restorations are increasing. Because their soils represent large carbon (C) and nitrogen (N) pools, they may produce significant amounts of CO₂ and N₂O depending on the plant species used in restorations. In addition, warming and N deposition may impact soil CO₂ and N₂O emissions from restored meadows.

Materials and methods

We collected soils from degraded meadows and plots restored using three different plant species at Wugong Mountain (Jiangxi, China). We measured CO₂ and N₂O emissions when soils were incubated at different temperatures (15, 25 or 35 °C) and levels of N addition (control vs. 4 g m^?2) to understand their responses to warming and N deposition.

Results and discussion

Dissolved organic C was higher in restored plots (especially with Fimbristylis dichotoma) compared to non-restored bare soils, and their soil inorganic N was lower. CO₂ emission rates were increased by vegetation restorations, decreased by N deposition, and increased by warming. CO₂ emission rates were similar for the three grass species at 15 and 25 °C, but they were lower with Miscanthus floridulus at 35 °C. Soils from F. dichotoma and Carex chinensis plots had higher N₂O emissions than degraded or M. floridulus plots, especially at 25 °C.

Conclusions

These results show that the effects of restorations on soil greenhouse gas emissions depended on plant species. In addition, these differences varied with temperature suggesting that future climate should be considered when choosing plant species in restorations to predict soil CO₂ and N₂O emissions and global warming potential.